1. Field of the Invention
The invention relates to a process for rolling flat material and strip in a roll stand having work rolls and support rolls and having devices for balancing the work rolls, positively bending the work rolls and negatively bending the work rolls. The devices include vertically arranged piston-cylinder units that, resting bilaterally on the roll stand, are placed from above and below against projections embodied on chucks of the work rolls and extending toward the housing window. The piston-cylinder units may, depending on their pressurization, urge the chucks of the work rolls toward or away from each other.
2. Description of the Related Art
In four-high roll stands, various adjustment elements are available to influence the roll gap and the strip profile. These adjustments include positive and negative bending devices for the work rolls. The plane of the vertical roll gap between the work rolls may be bent or curved by hydraulic cylinders in both directions via their longitudinal axes. The positive and negative bending devices allow the cross-sectional profile of the rolled material to be adjusted or changed within certain limits.
The "positive" bending is accomplished using piston-cylinder units that also serve to balance the rolls and are placed directly or indirectly in the housing window of the roll stands, for example, in hydraulic blocks. Located in these hydraulic blocks or in active connection with the support roll chucks are the piston-cylinder units for "negative" bending, with which the rolls may be bent in the sense of a convex cross-sectional contour of the roll gap.
A problem with the prior art devices is that the negative bending devices are not activateable until the material to be rolled has entered the roll gap. To pressurize the piston-cylinder units for negative work roll bending, a roll load must exist. Otherwise contact between the work rolls and support rolls is not guaranteed. This requirement that the material actually enter the roll gap before the adjustment of the negative bending results in non-standard lengths of strip at the beginning and end portions of the material to be rolled. These beginning and end portions of the material to be rolled cannot be sold and are considered lost pieces. These lost pieces detract from the profitability of the roll mill. The amount of lost strip is considerable, due to the time needed for the switching and control procedures involved with setting the negative bending device.